Carbon dioxide emission plumes from a large power station detected from space

Researchers at the Finnish Meteorological Institute developed a new methodology to derive source-specific NOₓ-to-CO₂ emission ratios using satellite observations. The method was applied to Matimba power station in South Africa. The results can be used to estimate carbon dioxide emissions.

Since the Paris agreement was adopted in 2015, the role of satellite observations in understanding anthropogenic CO₂emissions has become increasingly important. Currently, the NASA’s CO₂ instrument Orbiting Carbon Observatory-2 (OCO-2), launched in 2014, provides CO₂ observations with the best coverage and resolution. However, the observations are obtained on a narrow swath (less than 10 km), which does allow the detection of the cross-sections of the emission plumes, but not the plumes in their entirety. Satellite observations of co-emitted species, such as NO₂, facilitate the detection of the CO₂ emission plumes. The European Commission is currently planning a new CO₂ monitoring mission CO2M via the Copernicus Programme, which will observe both CO₂ and NO₂ over a larger swath (over 250 km).

OCO-2 and TROPOMI observations near Matimba power station (red triangle) in South Africa between May 2018 and November 2020. Image: Hakkarainen et al. 2021. CC BY 4.0.

Estimating CO₂ emissions from individual sources using satellite data can be challenging due to the large background levels, while it is easier for short-lived gases like NO₂. In a recently published study, a new methodology to calculate source-specific NOₓ-to-CO₂ emission ratio from satellite observations is developed. This ratio provides information on how clean the employed technology is and can be used to convert NOₓ emission into CO₂ emission. The method was tested for the Matimba power station in South Africa, which is an optimal case study as it is a large emission source with several satellite overpasses, and it is also well isolated from other sources.

The results are based on the CO₂ observations from the NASA’s OCO-2 satellite and the NO₂ retrievals from the European TROPOMI (TROPOspheric Monitoring Instrument), operating onboard the Sentinel 5 Precursor satellite since late 2017. During the 2018–2020 period, 14 collocations over Matimba enabled the simultaneous detection of the CO₂and NO₂ plumes. The mean NO_x-to-CO₂ emission ratio was estimated as (2.6 ± 0.6) × 10^-3 and the CO₂ emission as 60 kton/day. The obtained CO₂ emission estimates are similar to those reported in existing inventories such as ODIAC.

The research was carried on in the DACES project, which focuses on detecting anthropogenic CO₂ emissions sources by exploiting the synergy between satellite-based observations of short-lived polluting gases (such as NO₂) and greenhouse gases.

The full publication by Hakkarainen and co-authors can be found at the following link:https://doi.org/10.1016/j.aeaoa.2021.100110